The Bafang Ultra mid drive is a bulletproof motor. It does rarely happen that a controller board needs to be changed. This video doesn't show the removal of the motor, (there are plenty of videos showing removal) but it shows how fairly easy it is to replace a bad controller. The new controller was purchased at Greenbikekit.com. When you replace a controller model Cr r10m.1000.Sn.u.1.5 you have to calibrate the motor to the new controller. I just found this out march 2022. You do this with the C961 display that has been programmed to go into diagnostic mode.